2 AIM ACCOUNTS in ICHAT

I have a IMac OSX. I currently have 2 aim accounts. I use one for my home use and one for business. When I first sigend up for MAIL and ICHAT I used my home email and home aim account. I logged on to my computer today, i saw that my business ichat account was logged in. I have no idea how I did this and no idea how to switch it back. Any help would be appreciated. Thank you.